1. Field of the Invention
The present invention relates generally to bone conduction devices, and more particularly, to infection prevention measures associated with percutaneous bone conduction devices.
2. Related Art
Bone-anchored medical implant systems are used to connect or fixate hearing devices to a recipient, directly to the bone or skull of the recipient. Some applications include hearing implants such as bone conduction devices marketed by Cochlear Bone Anchored Solutions AB in Sweden. Such bone conduction devices sometimes comprise, in the case of percutaneous bone conductions devices as is shown by way of example in FIG. 27d in black-box format, an external, removable unit 2759 including a vibrator 2761 which transforms sound into mechanical vibrations. Percutaneous bone conductions devices conduct those mechanical vibrations via an abutment 2763 and a bone fixture 2765 of the implant, into the bone of the skull. Passive transcutaneous bone conduction devices conduct those mechanical vibrations through skin of the recipient to an implantable component which includes a bone fixture. The vibrations are transmitted mechanically via the skull bone and thereafter to the inner ear of a person with impaired hearing and allows for the hearing organ to register the sound. A hearing device of the bone conduction device type typically includes an anchoring element or fixture, in the form of, for example, an implanted titanium screw, corresponding to the bone fixture, installed in the bone behind the external ear and the sound is transmitted via the skull bone to the cochlea (inner ear), irrespective of any disease, injury or other dysfunction of the middle ear. In percutaneous bone conduction or anchoring arrangements, the skin is penetrated, which makes the vibratory transmission very efficient. This arrangement can also be used in connection with facial prostheses, such as, for example, some of those marketed by Cochlear Limited, Australia.
The implants which are used with percutaneous bone conduction devices are sometimes provided in two pieces. One piece comprises the screw-shaped anchoring element (fixture or anchor) and the other piece comprises the abutment, which penetrates the skin. This two-piece design, in many exemplary embodiments, allows the surgical implantation to be carried out as a two-step procedure. In the first step of implanting such a two-pieced design, the fixture is inserted and maintained unloaded during a healing period of some months or so. After this healing period the second step of the surgical procedure, i.e. the connection of the abutment by means of an abutment screw, is executed. The two-part design may allow for the implants to be up-graded, if desirable, without removing the fixture or anchor. Furthermore, if the abutment is damaged, it can then be replaced without need of removal of the bone anchored screw or fixture.
A situation sometimes experienced with bone conduction devices in general, and percutaneous implant devices in particular, is the risk of infections and inflammation. This exists sometimes at the tissue-implant interface. The infections are a result of bacterial colonization at the area around the interface between the bone fixture and the abutment. This problem can be persistent and cause infections. Cleaning of the interface has utility, but even regular cleaning and disinfection is not always entirely successful. The risk of infections may also exist at the interface between separate components of totally implantable prostheses.
With respect to a percutaneous bone conduction device, the bacteria may enter the implant-tissue interface by two different routes—an external route on the external surface of the abutment, and an internal route which starts at the top of the abutment and travels via internal parts (screw connection) of the implant system and may exit at the abutment-fixture-soft tissue junction or interface. The external route is the most open route, but the bacteria may also reach the implant-tissue interface from the internal route, known as the internal micro-leakage pathway.